Basic reproduction number

Values of R0 of well-known diseases
Disease R0
Measles 12–18
Whooping cough 12–17
COVID-19 (Omicron variant) 9.5–20
Chickenpox 10–12
Mumps 10–12
Norovirus 7.2–14
Rubella 6–7
COVID-19 (Delta variant) 5–9.5
Polio 5–7
Smallpox 3.5–6.0
HIV/AIDS 2–5
COVID-19 (ancestral strain) 2.4–3.4
Common cold 2–3
Mpox 2.1–2.7
Ebola 1.4–1.8
Flu (2009 pandemic strain) 1.6 (1.3–2.0)
Seasonal flu 1.3 (1.2–1.4)

A very important number for describing whether a disease can become an epidemic or not is R0, pronounced "R naught" or "R zero". It refers to how many people a person who has this disease is expected to infect on average if there are no people immune to the disease. It is an abbreviation for basic reproduction number.

If R0 > 1, a disease can become an epidemic. If R0 < 1, it cannot. Most commonly known diseases have R0 > 1. However, vaccines can be used to make enough people immune in a population to stop epidemics from happening. We can also use other measures to make the effective reproduction rate (Re, usually written Rt with t for time) lower than the basic reproduction rate (R0).

An example of a vaccine that works really well is the smallpox vaccine, which stopped smallpox virus from spreading so well that it no longer exists except in laboratories. Examples of making the effective reproduction rate lower than the basic reproduction rate are using condoms to stop sexually transmitted diseases from spreading or not getting close to others (physical distancing, often called social distancing) to stop respiratory diseases from spreading.

References

  1. 1 2 From a module of a training course with data modified from other sources.
  1. ↑ Guerra FM, Bolotin S, Lim G, Heffernan J, Deeks SL, Li Y, Crowcroft NS (December 2017). "The basic reproduction number (R0) of measles: a systematic review". The Lancet. Infectious Diseases. 17 (12): e420–e428. doi:10.1016/S1473-3099(17)30307-9. PMID 28757186.
  2. ↑ Delamater PL, Street EJ, Leslie TF, Yang YT, Jacobsen KH (January 2019). "Complexity of the Basic Reproduction Number (R0)". Emerging Infectious Diseases. 25 (1): 1–4. Bibcode:2019EIDis..25....1D. doi:10.3201/eid2501.171901. PMC 6302597. PMID 30560777.
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  4. ↑ Liu, Y (9 March 2022). "The effective reproductive number of the Omicron variant of SARS-CoV-2 is several times relative to Delta". Journal of Travel Medicine. 29 (3). Table 1. doi:10.1093/jtm/taac037. ISSN 1708-8305. PMC 8992231. PMID 35262737.
  5. ↑ Zhang Z (14 October 2023). "Omicron's intrinsic gene-gene interactions jumped away from earlier SARS-CoV-2 variants and gene homologs between humans and animals". Advances in Biomarker Sciences and Technology. 5 (2023): 105–123. doi:10.1016/j.abst.2023.09.002.
  6. ↑ Prater E (9 July 2022). "Move over, measles: Dominant Omicron subvariants BA.4 and BA.5 could be the most infectious viruses known to man". Fortune. Retrieved 26 November 2025.{{cite web}}: CS1 maint: deprecated archival service (link)
  7. ↑ Ireland's Health Services. Health Care Worker Information (PDF). Archived from the original (PDF) on 2020-03-26. Retrieved 2020-03-27.
  8. ↑ Australian government Department of Health Mumps Laboratory Case Definition (LCD)
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  10. ↑ Centers for Disease Control and Prevention; World Health Organization (2001). "History and epidemiology of global smallpox eradication". Smallpox: disease, prevention, and intervention (training course) (Presentation). Atlanta: Centers for Disease Control and Prevention (published 2014-08-25). cdc:27929. Archived (PDF) from the original on 2017-03-17. Retrieved 2021-06-17.
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  12. ↑ Luman, ET; Barker, LE; Simpson, DM; Rodewald, LE; Szilagyi, PG; Zhao, Z (May 2001). "National, state, and urban-area vaccination-coverage levels among children aged 19–35 months, United States, 1999". American Journal of Preventive Medicine. 20 (4): 88–153. doi:10.1016/s0749-3797(01)00274-4. PMID 12174806.
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  14. ↑ McMorrow, Meredith (July 29, 2021). "Improving communications around vaccine breakthrough and vaccine effectiveness". p. 15. Archived from the original on January 25, 2022. Retrieved July 30, 2021.
  15. ↑ Gani R, Leach S (December 2001). "Transmission potential of smallpox in contemporary populations". Nature. 414 (6865): 748–51. Bibcode:2001Natur.414..748G. doi:10.1038/414748a. PMID 11742399. S2CID 52799168. Retrieved 18 March 2020.
  16. ↑ "Playing the Numbers Game: R0". National Emerging Special Pathogen Training and Education Center. 30 January 2020. Archived from the original on 12 May 2020. Retrieved 27 December 2020. [...] while infections that require sexual contact like HIV have a lower R0 (2-5).
  17. ↑ Billah, Arif; Miah, Mamun; Khan, Nuruzzaman (11 November 2020). "Reproductive number of coronavirus: A systematic review and meta-analysis based on global level evidence". PLOS ONE. 15 (11) e0242128. Bibcode:2020PLoSO..1542128B. doi:10.1371/journal.pone.0242128. PMC 7657547. PMID 33175914.
  18. ↑ Reis J; Shaman J (19 March 2018). "Simulation of four respiratory viruses and inference of epidemiological parameters". Infectious Disease Modelling. 3: 23–34. doi:10.1016/j.idm.2018.03.006. PMC 6326234. PMID 30839912.
  19. ↑ Shabir O (16 February 2021). "What is R0?". News-Medical.Net. Archived from the original on 1 June 2025. Retrieved 1 December 2025.
  20. ↑ Grant R, Nguyen LL, Breban R (2020-09-01). "Modelling human-to-human transmission of monkeypox" (PDF). Bulletin of the World Health Organization. 98 (9): 638–640. doi:10.2471/BLT.19.242347. ISSN 0042-9686. PMC 7463189. PMID 33012864. Archived from the original (PDF) on 11 December 2020.
  21. ↑ Al-Raeei M (February 2023). "The study of human monkeypox disease in 2022 using the epidemic models: herd immunity and the basic reproduction number case". Annals of Medicine & Surgery. 85 (2): 316–321. doi:10.1097/MS9.0000000000000229. ISSN 2049-0801. PMC 9949786. PMID 36845803.
  22. ↑ Wong ZS, Bui CM, Chughtai AA, Macintyre CR (April 2017). "A systematic review of early modelling studies of Ebola virus disease in West Africa". Epidemiology and Infection. 145 (6): 1069–1094. doi:10.1017/S0950268817000164. PMC 9507849. PMID 28166851. The median of the R0 mean estimate for the ongoing epidemic (overall) is 1.78 (interquartile range: 1.44, 1.80)
  23. ↑ Fraser C, Donnelly CA, Cauchemez S, Hanage WP, Van Kerkhove MD, Hollingsworth TD, et al. (June 2009). "Pandemic potential of a strain of influenza A (H1N1): early findings". Science. 324 (5934): 1557–61. Bibcode:2009Sci...324.1557F. doi:10.1126/science.1176062. PMC 3735127. PMID 19433588.
  24. ↑ Chowell G, Miller MA, Viboud C (June 2008). "Seasonal influenza in the United States, France, and Australia: transmission and prospects for control". Epidemiology and Infection. 136 (6). Cambridge University Press: 852–64. doi:10.1017/S0950268807009144. PMC 2680121. PMID 17634159. The reproduction number across influenza seasons and countries lied in the range 0.9–2.0 with an overall mean of 1.3, and 95% confidence interval (CI) 1.2–1.4.